Reactivity of germ cell maturation stage-specific markers in spermatocyticseminoma: Diagnostic and etiological implications

It is generally accepted that testicular seminomas and spermatocytic semino mas have separate pathogeneses, although the origin of these two types of g erm cell tumors of the adult testis remains a matter of debate. Although an embryonic germ cell origin seems to be most likely for seminomas, a sperma togonia-spermatocyte origin has been suggested for spermatocytic seminoma. To shed more light on the etiology of spermatocytic seminomas, we undertook an immunohistochemical and molecular approach using SCP1 (synaptonemal com plex protein 1), SSX (synovial sarcoma on X chromosome), and XPA (xeroderma pigmentosum type A) as targets. Although a stage-specific expression patte rn has been reported for SCP1 and SSX in normal spermatogenesis, we demonst rate here that it also exists for XPA. In fact. immunohistochemistry shows that the proteins of SCP1 and XPA are specifically present in the stage of primary and pachytene spermatocytes. In contrast, SSX was found in spermato gonia and primary spermatocytes, as well as in germ cells, from at least th e 17th week of intrauterine development onward. Although no protein encoded by any of these genes was detected in tumor cells of a series of testicula r seminomas, all tested spermatocytic seminomas were positive, in agreement with expression analysis. These data support the model that seminomas orig inate from an embryonic germ cell, and they imply that the cell of origin o f spermatocytic seminomas is at least capable of maturing to the stage of s permatogonia-pachytene spermatocyte.